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Perceptual OrganizationPerceptual ConstanciesDepth and DimensionPerceptual SetThe World of Illusions

Perception

Which center circle is larger?

Here are the same circles again.

Gestalt Principles of Visual Perception


Gestalt – Movement in experimental psychology which began prior to WWI.

We perceive objects as well-organized patterns rather than separate components.

“The whole is greater than the sum of it’s parts.”

Based on the concept of “grouping”.


We impose visual organization on stimuli

W.E. Hill, 1915 German postcard, 1880


Illusory Contours

The Kanisza triangle as figure-ground illusory contours


Three Main Principles:

Grouping (proximity, similarity, continuity, closure)

Goodness of figuresFigure/ground relationships


Grouping:

Law of Proximity


Grouping:

Law of Similarity


Grouping: Law of Similarity: Shape, Scale, Color


Law of Good Continuation, or Continuity

Objects arranged in either a straight line or a smooth curve tend to be seen as a unit.


Law of Closure


Law of Common Fate

Chapter 7 - Perception 18

The Law of Common Fate

Finally, elements of visual perception that move togetherare seen as forming a common object.

This law is best imagined in terms of those animals yousee on nature shows that seem to perfectly blend intotheir background, until they move. Then suddenly theyappear visible.

As an example though ...


Common Fate Example - 1


Goodness of Figure, or the Law of Pragnanz

(Pragnanz is German for Pregnant, but in the sense of pregnant with meaning, not with child!)


Figure/Ground relationships

Figure – seen as the foreground

Ground – seen as the background

Contours – “belong” to the figure


Reversible Figure/Ground

relationship



relationship

Can be affected by the principle of smallness:

Smaller areas tend to be seen as figures against a larger background.



Relationship:

Tessellation – interlocking figure/ground

M.C. Escher


Gestalt laws of Grouping organize the visual scene into units

The Law of Pragnanz, or Goodness of Figure creates the simplest most meaningful pattern

Figure/Ground relationships define important parts of the scene


Problems with Gestalt theory:

It is a phenomenological approach

Some of the terms are vague

(e.g. what is the “simplest” organization?)

Drawings that one can perceive in different ways by reversing figure and ground.


Perceptual Organization Reversible Figures

Proximity Seeing 3 pair of lines in

A Similarity

Seeing columns of orange and red dots in B

Continuity Seeing lines that

connect 1 to 2 and 3 to 4 in C

Closure Seeing a horse in D


Perceptual Organization Gestalt Laws of Grouping

Geons (geometric icons) are simple 3D component shapes.

A limited number are stored in memory.

Geons are combined to identify essential contours of objects.


Perceptual OrganizationIdentifying Objects

Size Constancy The tendency to view an object as

constant in size despite changes in the size of the retinal image.

Shape Constancy The tendency to see an object as

keeping its form despite changes in orientation.


Perceptual Constancies

Perceptual Constancies The Ames

Room A specially-built room that makes people seem to change size as they move around in it

The room is not a rectangle, as viewers assume it is.

A single peephole prevents using binocular depth cues.


Even though these images cast shadows of different shapes, they still are seen as round.


Perceptual Constancies Shape Constancy

Depth Perception The use of visual cues to estimate

depth and distance. Convergence

A binocular cue involving the turning inward of the eyes as an object gets closer.

Binocular Disparity A binocular cue whereby the closer an

object is, the more different the image is in each retina.


Depth and Dimension

Distance cues that enable the perception of depth with one eye. Relative Image Size Linear Perspective Interposition Atmospheric Perspective Relative Elevation Familiarity


Depth and DimensionMonocular Depth Cues


Depth Perception

In order for us to figure out where an objects is, we need someway of judging depth in our visual environment.

In turns out that we use a fairly large range of cues to helpin our perception of depth, and the fall under two generalclasses.

Some depth information can only be obtained when both eyes are viewing the world … these types of information are termedbinocular cues to depth.

In contrast, monocular cues can be obtained using only one eye.


Binocular Cues - ConvergenceBecause the two eyes converge on an object when we areviewing it, the brain can use the angle of convergence as acue to how far away that object is. For example:

The larger the angle, thenearer the object


Binocular Cues - Retinal DisparityWhenever we are not focusing on an object, the image of thatobject falls on different points of the two retinas.

The amount of disparity (difference) between the two retinalimages can be used as a cue for distance.

Try holding up two fingers one in front of the other. Focus onthe front one (you should now see two images of the back one).Now move the back one away from, then back towards you, while still focusing on the front one. What happens to the twoimages you see as the back finger moves?


Monocular Cues - InterpositionWhen one object partially occludes our view of a secondobject, we assume that the first object is closer to us thatthe second.

For example:

Vs.


Monocular Cues - PerspectiveThings appear to get smaller as they recede into the distanceeven though we know they are not actually getting smaller.

Given this, if the general size ofsome object in the scene is known,the size of the retinal image castby that object can be used to judgeits distance from us.

This can sometimes lead to neat illusions such as the one tothe right.


Monocular Cues- Shading

We live in a world where our major light sources tend to come from above. As a result, shading has come to be anothersource of depth information such that objects that are shadedlighter on the top are seen as “sticking out towards us”.

Devised by Eleanor Gibson and Richard Walk to test depth perception in infants and animals.

Provides visual illusion of a cliff.

Caregiver stands across the gap.

Babies are not afraid until about the age they can crawl.


Depth and Dimension The Visual Cliff

What is seen in the center figures depends on the order in which one looks at the figures: If scanned from the left, a man’s face is seen. If scanned from the right, a woman’s figure is seen.


Perceptual Set

The same physical stimulus can be interpreted differently depending on perceptual set, e.g., context effects.

When is the middle character the letter B and when is it the number 13?


Perceptual Set Context Effects

Illusion in which the perceived length of a line is altered by the position of other lines that enclose it


The World of Illusions The Müller-Lyer Illusion

Illusion in which the perceived line length is affected by linear perspective cues.

Side lines seem to converge

Top line seems farther away But the retinal

images of the red lines are equal.


The World of Illusions The Ponzo Illusion

The Case for ESPThe Case against ESPThe Continuing Controversy

Extrasensory Perception

Extrasensory Perception (ESP) The ability to perceive something

without ordinary sensory information. This has not been scientifically

demonstrated. Parapsychologists distinguish between

three types of ESP: Telepathy – Mind-to-mind communication Clairvoyance – Perception of remote events Precognition – Ability to see future events


The Case for ESP

Of course, there is also psychokinesis.

And Levitation Paranormal healing Luminiscent Phenomena (aura) OBE- or sometimes OOBE (An out-of-

body experience )


Are they real?

Scientist usually conclude that there is no strong scientific support for these type of phenomena.

Perhaps this is because they defy the establishment in psychology.

Perhaps it is because it is simply a lie… Anyway, there is an amazing instrument

inside our heads that is fascinating enough to start investigating…

J. B. Rhine conducted many experiments on ESP using stimuli such as these.

Rhine believed that his evidence supported the existence of ESP, but his findings were flawed..


The Case against ESPESP Cards

Online tests

http://www.psychicscience.org/esp3.aspx

http://www.psychic-experiences.com/psychic-tests/zener-cards.php

http://www.leotarot.com/test-extrasensorial-percepcion-adivinacion-intuicion-gratis.html

Hallucinations, delusions and illusions

Hallucination: is a perception in the absence of a stimulus. Usually present in severe mental disorder but also in delerium tremens, sleep deprivation and drug use or abuse.

Delusions: an erroneous belief that is held in the face of evidence to the contrary “aliens control my body” “the end of the world is near” “you are cheating on me, the bed is still warm” “I am responsible for last week´s earthquake” “Barak Obama has a crush on me…” “I am Jesus, do you want to be the 13th apostle?” “I have parasites in my eyes, I can see them” “I am the king of England” “The government is conspiring to kill me…”

Illusions:is the mis-perception or misinterpretation of real external stimuli

Example: You recognize a message “hidden” in a

song.

Este tipo de espejismo surge porque las capas de aire junto a la superficie de la Tierra se han vuelto calientes y, por lo tanto, menos densas que las capas más altas. Los rayos de luz junto al suelo se curvan bruscamente hacia arriba y el «agua», que parece mostrar los «reflejos» de objetos distantes, es la imagen del cielo.

Pareidolia

Pareidolia

http://facesinplaces.blogspot.com/

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